1. Field of the Invention
The present invention relates to a method and apparatus for displaying data, such as topographical data, and to a computer program for enabling display of such data. More particularly, the present invention relates to displaying data, such as topographical data, for efficient representation of data in a low-cost portable hand-held device.
2. Description of the Related Art
Portable mapping devices such as GPS (Global Positioning System) and PDAs (Personal Digital Assistants) are capable of displaying and manipulating digital maps. In addition to the roads, streets, rivers, lakes and other geographic features, these maps often display topographical information as well. However, topographical information is presented only as a set of topographical lines similar to the one that are used in conventional paper topographical maps. Therefore, a true value of the terrain elevation is known and stored only for the topographical lines that are stored for the map, e.g.xe2x80x94Garmin Hand-Held GPS Vista device. This makes it difficult to compute elevation at other points or to create new topographical lines for the elevation levels that are not pre-stored for the map. This also requires a large data storage if topographical lines with a high resolution are required.
At the same time, digital technology allows one to store in a computer and to manipulate a true 3D (3 Dimensional) digital elevation model where the elevation of any terrain point can be computed. However, up to now, such systems were available only for use with powerful PC (Personal Computer) machines having a lot of memory and significant processing power, e.g.xe2x80x94DeLorme Topo USA PC product.
U.S. Pat. No. 5,902,347, to Backman et al. and entitled Hand-held GPS-mapping Device, discloses a hand-held GPS mapping device containing a GPS receiver, a database capable of storing vector or bit-mapped graphics, a viewing port, an embedded processor, a simplified user interface, a data compression algorithm, and other supporting electronics.
U.S. Pat. No. 5,902,347, to Backman et al. discloses two features, namely, a device that allows to view map images in the bright sun light and a device which divides a bit image of a topographical map by tiles and then compresses each tile with regular image compression algorithins such as TIFF (Tagged Image File Format).
The first device is not relevant to the present invention. As to the second device, while the abstract thereof mentioned vector maps, this is only to include such map images under the first devicexe2x80x94having a screen that can be viewed outside. The tile compression method of the second device is applicable only to the bit map imagesxe2x80x94photo images, of the map, that is, so called raster maps.
The Detailed Description of U.S. Pat. No. 5,902,347, to Backman et al. describes in much detail how a photo image of a map is divided into tiles and then compressed with TIFF. There is no discussion about any digital maps. In fact, a digital map cannot be divided into tiles by simply cutting a whole map. A digital map is built out of tiles from the beginning and they are usually not compressed in a conventional sense but are bit encoded to provide a maximum speed of map reconstruction.
By the time of the issuance of U.S. Pat. No. 5,902,347, to Backman et al., there were several commercial handheld GPS systems capable of displaying vector maps on the device screen. One of such devices, Nav 6000, was produced by Magellan from 1996. These vector maps were constructed from the tiles.
The present invention is not concerned with a bit image or with a vector map. Rather, the present invention deals with Digital Elevation Model data, which is a quite different from both. DEM allows computing true elevation in any point of the map while a photo image of a map does not allow retrieving any digital information about features such as road direction or elevation, etc.
In addition, the present invention allows one to create tiles of different size with different resolution of data, which depend on the zoom level where these tiles are intended to be used. Image data cannot be simply thinned out so creation of tiles with different internal resolution of the data is impossible and is not even mentioned in U.S. Pat. No. 5,902,347, to Backman et al.
In accordance with one aspect of the present invention, a cell compression structure is utilized such that each cell can be decompressed independent of the others. Then, the data can be decompressed on-the-fly only for those cells that are needed to provide data for the area displayed on the screen of the device and only for the zoom levels that are currently used.
In accordance with another aspect of the present invention, elevation data, for example, is compressed using off-line processing. An asymmetrical compression algorithm is utilized so as to emphasize simplicity in the decompression of the data by providing most of the processing during the off-line data compression, thereby allowing the use of high-power computing devices to compress the data and allowing simple display devices having limited computing capabilities to decompress the data.
In accordance with still another aspect of the present invention, lossy compression is utilized to increase the data compression ratio. Both the average (rms) and maximum data compression error or the average (rms) and relative data compression error are controlled. The limitation on the absolute data compression error may be achieved by storing explicit corrections for the grid points where a good fit cannot be achieved with a desired level of data compression.
In accordance with another aspect of the present invention, data is decompressed and recomputed to a new grid, which is parallel to the screen and with a grid step, which is comparable with the screen size and resolution of a map presentation on the screen. This allows quick image rotation for the xe2x80x9ctrack upxe2x80x9d map orientation as well as providing better performance by effectively reducing the number of grid points to the minimum necessary for a given screen size and resolution.
In accordance with yet another aspect of the present invention, the topographical lines, for example, are computed on-the-fly using the screen reference grid of the new grid noted above. The elevation lines step is created on-the-fly and can either be user-specified or automatically determined from the map scale.
In accordance with another aspect of the present invention, the elevation value can be determined in real-time for any map location presented on the display screen.
Lastly, in accordance with still another aspect of the present invention, the user can view an elevation profile of a selected road, street, trail, track, or any other line feature and can view an elevation profile along the line of travel or perpendicular to the line of travel or at any arbitrary angle with respect to the line of travel and at any distance from the current position.
These and other objects of the present invention may be effected by providing a portable hand-held data display device comprising: a CPU (Central Processing Unit); an entry device, a memory, and at least one RAM (Random Access Memory), a map data storage device such as SD card or similar device, all operatively connected to said CPU; optionally, a GPS (Global Positioning System) unit, operatively connected to said CPU, to receive GPS signals and generate, with or without help of the CPU a digital output to said CPU indicative of a position location of said display device in response to said received GPS signals or a receiver to receive a digital output indicative of a position location to be displayed on said display device; and a video controller and a display screen, said video controller to receive signals from said CPU and to output signals to said display screen to produce an image on said display screen in response to said received signals from said CPU; wherein true digital elevation data, for example, is arranged to be stored as compressed cells in said memory, said CPU decompressing on-the-fly only data of cells needed to provide elevation data for an image area displayed on said display screen.
Note, that the current invention allows one to decompress and to display DEM data in a small hand-held device, such as PDA, that does not have direct position information from a GPS subsystem, internal or external. However, real time position information obtained from GPS allows the afore-said device to decompress, to restore, and to display topographical data that is relevant to the actual user position without any direct intervention by the user. Otherwise, such a device can display only topographical information for the area explicitly selected by the user. Such area may or may not be related to the current position of the user.
Also note that a user of the device always has an option to directly command the device to display topographical information about an area of his/her choosing even if a GPS subsystem is present and active.
These and other objects of the present invention may also be provided by effecting a method of displaying data on a screen of a portable hand-held device, the method comprising: a optionally receiving GPS (Global Positioning System) signals and generating a digital output indicative of a position location of said display device in response to said received GPS signals or otherwise generating a digital output indicative of a location to be displayed on said display device to produce an image on a display screen of the device in response to said digital output; and storing true digital elevation data, for example, as compressed cells and decompressing on-the-fly only data needed to provide elevation data for an image area displayed on said display screen.
The these and other objects of the present invention may yet further be provided by effecting program storage device, readable by a machine and tangibly embodying a program of instructions executable by the machine to perform method steps for displaying data on a screen of a portable hand-held device, the method comprising: receiving GPS (Global Positioning System) signals and generating a digital output indicative of a position location of said display device in response to said received GPS signals or otherwise generating a digital output indicative of a location to be displayed on said display device to produce an image on a display screen of the device in response to said digital output; and storing true digital elevation data, for example, as compressed cells and decompressing on-the-fly only data needed to provide elevation data for an image area displayed on said display screen.